Improve validation of openedx_content to prevent creation of corrupt states

[bradenmacdonald]

This PR implements tests for four of the issues identified in #463 .

1. set_draft_version() should reject a PublishableEntityVersion that belongs to a different PublishableEntity.
2. publish_from_drafts() should reject drafts that don't belong to the specified LearningPackage.
3. create_publishable_entity_version() should reject dependencies that are from a different LearningPackage.
4. publish_all_drafts() and publish_from_drafts() should not be callable from within a bulk_draft_changes_for() context.

Another issue is in a separate PR for simplicity: #569

Two issues are unaddressed as they are API design choices: create_publishable_entity_version() and create_publishable_entity() can both create either a useless or an invalid state if they are used on their own without corresponding [Component/Container/etc.] versions.

Platform: no corresponding changes are required in openedx-platform as far as I can tell.

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[bradenmacdonald]

Since it's hard to tell from the diff what's going on here:

This test_reset_drafts_to_published_bulk just called test_reset_drafts_to_published() inside bulk_draft_changes_for but that inner test does some setup, a publish, more setup, then a revert, so this was causing an error - we don't want to allow publishes inside bulk_draft_changes_for.

The refactored test is almost exactly the same, but is parametrized and when bulk=True it wraps the pre-publish setup in a bulk transaction, and the post-publish setup+revert in a second bulk transaction.

I think this is an even better test now because we can assert that the net effect of the second bulk transaction is zero, as it reverts to the published version.

My local git client shows the diff more cleanly than GitHub:

[ormsbee]

Minor request on more detail in the errors being raised.

[ormsbee]

[Comment]: I've generally used ValueError instead of ValidationError for invalid arguments, though I realize that doesn't make sense for things like checking that you're not in a bulk change context before publishing. Should I switch over, do you think?

[bradenmacdonald]

For these errors that are more developer-facing (you coded something wrong, not the user gave invalid input), I honestly don't think it makes much difference. I'm on the fence and happy to change to ValueError too if you'd like.

The python docs say

ValueError: Raised when an operation or function receives an argument that has the right type but an inappropriate value, and the situation is not described by a more precise exception

So I guess it depends if you consider ValidationError to be more precise. We could also define a custom exception that's even more specific, but I don't think it's worth it if we expect these to be pretty rare.

[bradenmacdonald]

@ormsbee I added in that extra logging you requested.

[ormsbee]

@bradenmacdonald, @kdmccormick: Just a heads up that something here is causing test failures in the modulestore migrator code.